Multichannel signaling system



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QN mw Feb. 3, 1953 Filed OCT.. 21, 1.948

M. M. LEVY Erm. 2,627,553

MULTICHANNEL SIGNAL-LING SYSTEM 4 Sheets-Sheet 2 P eb; 3, 1953 Filedoct. 21, 1948 Feb. 3, 1953 M. M. LEVY Erm. 2,627,553

MLTICHANNEL. SIGNALLING SYSTEM Filed Oct. 2l, 1948 4 Sheets-Sheet 5 -wwnaw/s ULA/mmv 7 Arme/vn Feb. 3, 1953 M. M. LEVY ETAL 2,627,553

MULTICHANNEL SIGNALLING SYSTEM Filed oct. 21. 194s 4 sheets-sheet 4Patented Feb. 3, 1953 MULTlCHANN EL SIGNALING .SYSTEM i l ll/Iaurice4`Moise Levy, Earls Court, and. Dennie Clark Esplney, North Wembley,England, assignors to The General Electric Company, Limited;Y

London, England Application October 21, 1948, Serial No, 55,732

InGreat-Britain November 21,1946,

9 Claims.

The present invention relates to multi-channel signalling systemsemploying modulated pulses and has for its principal object to increasethe numberof channels which can be employed with a given complexity of`apparatus or to enable simpler apparatus to be used for a given numberof channels.

Such arrangements for multi-channel signalling usually comprise adistributor which generates N trains of selector pulses at a suitablerecurrence frequency F cycles per second which is the same for all thetrains, N being the number of channels. The N trains are interlaced withone another, in other words the pulses of each train are time-delayedrelatively to those, of the preceding train. t In order to employ themaximum possible number of channels, the duration of the selector pulses`in seconds is made equal to, or only slightly less than 1/NF. A numberor" modulators, equal to the number N of channels, is provided and eachproduces modulatedpulsesI at the same frequency F.

For systems employing large numbers of pulses, the apparatus becomesvery complicated, For instance kone known form of` modulator is of theelectronic distributor type, comprisinga cathode ray tube having meansfor defiecting the cathode rayin a circular traclfover. a plate whichcontains a number of vslots equal; to the number of channels.These-slots arearranged to lie obliquely across the track of the cathoderay and when the cathode ray traverses each `slot electrons pass throughthe slot toa collecting electrode and a positive pulse is generated atthe plate owing to the cessation, or reduction, in the collection ofelectrons by the plate. Alternatively, use may be made of the negativepulses whichy are generated at the collecting electrode when the cathoderay traverses the slots. A number of deflecting means, such as pairs ofdeflecting plates, equal to the number of channels is provided and theseare so disposed that each co-operates with a diierent slot and candeflect the cathode ray, radially inwards and outwards, during thetimethe ray is passing over the correspondingtslot. In this way the instant(at, which the positive or negative pulse occurs can be varied inaccordance with a modulation voltage vand what is` known as timemodulation of thepulses is 0btained. Each deecting means with its slotcon- L 2. pulses of the several channels are separated and demodulated.

If` the number of channels is large, for instance 100 or more, it isevident that the distributormodulators becomecomplicated and diiiicultto manufacture and an electronic device of the kind above describedneeding say-100 channel modulators ,is probably not practical.

According to the present invention,- in a multichannel pulsesignallingsystem for operating N channels each ata recurrence frequencyF; there are provided N/a channel modulating or demodulating devices,each operating upon a different group of a, equally spaced channelswherec is an integer, and distributor means areprovided for couplingeach. channel to its associated modulator or demodulator at theappropriatetimes.

In the case oi modulation the said device may be either a device whichmodulates pulses in accordance with signals in the manner required fortransmission or performs at least one stepin such modulation; forinstance produces amplitudew modulated pulses-which are subsequently`conl verted to width-modulated pulses.` In the case of demodulatiomtheAsaid device is notone performing the final; demodulation but anintermediate step such for, example as the conversion of time-modulationinto width modulation.` in eithercase the invention enables theapparatus to be simplified considerably`.

The invention will be described by way of example with reference to theaccompanying drawings invwhich Figure l is a diagram illustrating theoperation of a l2() channelmodulating system according to the invention,

Figure 2 is a circuit diagram of such asystem,

Figures 3 ande showparts of .Figure A2 in greater detail and i Figure -5is a diagram illustrating -the operation of a `12() channel demodulatingsystem according `tothe invention.

Referring `to Figure 1,'there are shown at A channel pulses numbered I,3, 5` etc. to ile and then repeating, every pulse l ,i 3 etc. having a,re-f currence frequency 'of Ska/s.` Every2lthpulse is of largeramplitude and serves as a synchronising pulse. Pulses i are of differentcharacteristics from the remaining synchronisingpulses,,such as 25,49,13 etc.,- for instance as shown theyl may be wider, and serve forsynchronisation-at the chanel pulse repetition frequency. The -pulses`Si, 5 23;,2'!` 41 etc. inclusive aremodulated respectively, forrexample -in time, i with different channel signals.

' The square waveoscillation-B ci frequency 540 aceites kc./s. can beregarded as a train of pulses at a recurrence frequency of 540 kc./s.,these pulses defining the channel width allotted to each channel, inthis case about 0.925 microsecond.

Figure 1 shows at A the channel pulses for the odd numbered channels.There is a like number of even numbered channels 2, 4, 6 etc. and thetime intervals allotted to these are defined by pulses at 540 kc./s. ofopposite sense to the B pulses. Further synchronisingY pulses may beprovided for the even channels if desired and these may be spacedapproximately midway between those for the odd channels.

With this arrangement N=l20, F=9 kc./s. and the maximum width of achannel as dened by the pulses B is, as stated, about 0.925 microsecond.To avoid confusion with other reference numerals, channel pulses willhereinafter be referred to as A1, A: etc. and selecter pulses which denethe channel widths as B1, B3 etc.

Referring now to Figure 2, there is shown a master generator Igenerating a sine wave oscillation at a frequency of 45 kc./s. Thisoscillation is fed to a device II which amplies the oscillation andprovides at each of terminals I2, I3, I4 and I5 an output voltage at 45kc./s., the voltage at the terminals I4 and I5 leading that at theterminals I2 and I3 in phase by 90. Typical of phase-splitters whichwill cause the Voltage at the terminals I4 and I5 to lead the voltage atthe terminals I2 and I3 are apparatuses disclosed in the following:

Time Bases by O. S. Puckle (Chapman and Hall), page '16, Fig. 51, thecircuit including VE l e c t ri c a l Communication (InternationalStandard Electric Corporation) volume l18, No. 3, January 1940, page216, Figure l5; 90 phase shifter "Frequency Modulation by August Hund,New York 1942, Fig. 75 on page 242: 90 phase shifter.

The terminals I2 and I4 are connectedrespectively to devices IB and I'Iwhich serve to square the wave form. Examples of such squaring devicesare given in Radio Engineers Handbookby F. E. Terman, 1943, page 970,Fig. 76 and footnotes 3, 4 and 5. A square wave at 45 kc./s. thusappears at terminals I8 and I9 of device I6 and a second square wave ofthe same frequency but differing in phase by 90 appears at terminal 20of device I'I. The terminal I8 is connected to a multivibrator 2I actingas a frequency divider running at 9 kc./s. A suitable vibrator isexempliiied in the Radio Engineers Handbookabove referred to, page 512,Fig. 32 (a). The output of the device 2| is fed to a selective amplifier22 which provides at its output terminals 23 and 24 sine waveoscillations at 9 kc./s., that at 24 leadingthat at 23 by 90 in phase.The phase-splitting portion of the amplier 22 may be constructed in thesame manner as the corresponding part of the amplifier I I. Thefrequencies and relative phases of voltages at various points in thecircuit are marked on the drawing.

At 25 vand 26 are shown two distributors in the form of cathode raytubes. In these tubes the anodes D are disposed overlapping one anotherin two annular zones one within the other, the centres of the anodes inone zone lying radially opposite the centres of the spaces between theanodes in the other zone. The cathode ray is caused to rotate in aconical path and is deiiected radially to engage anodes in the two zonesalternately. In this way the rate of switching can be made independentof the speed of rotation of the cathode ray. Another advantage is that agreater number of anodes of given size can be accommodatedin a tube ofgivenV size.

In Figure 2, there are ten anodes D in each tube 25 and 26. The cathoderay is caused to rotate by two sinusoidal oscillations at 9 kc./s., 90

displayed in phase relatively to one another applied to the two pairs ofdeflecting coils 28 and 29 from terminals 23 and 24 respectively. Theray is deected radially by means of square wave oscillations at 45kc./s. applied from terminals i9 and 20 to outer conical electrodes 39and 3l respectively, the inner conical electrodes 32 and 33 beingearthed. The deection applied is such that the cathode ray is movedthereby from the outer anode zone to the inner anode zone and viceversa.

At 34 in Figure 2 is shown a cathode ray distributor-modulator tube ofknown type. In front of its collecting electrode 35 is arranged a plate35 having a number' of slots 45 as shown in Figure 4, whichl is a Viewin an axial direction of part of the right hand end of the tube 34 inFigure 2. The slots 45 are arranged in an annular zone and the essentialparts thereof are inclined at about to the circular centre line of thezone. As the cathode ray is swept over` these slots electrons passthrough and reach the collecting electrode 35 whichv thus receives aseries of negative pulses. In the present example there are twelve slotsand co-operating with each is a deflecting electrode M. These deflectingelec trodes are placed as shown in Figure 2 only for the sake ofclearness; in practice they are arranged as indicated' in Figure 4 in aring within the tube, each being near to the cathode ray when it engagesone'slot and being capable, when fed with signal voltage, of deflectingthe cathode ray radially in accordance with the signal and 'thus varyingthe instant at which the negative pulse is generated at the electrode35. The

, electrodes M cov-operate with an inner electrode M1, shown in Figure4, which may be common to all the electrodes M.

The cathode ray in thev tube 34 is caused to rotate by sine waveoscillations at 45 kc./s. fed from terminals I3 and I'5 to its two pairsof deflecting coils 37 and 38, the oscillations being mutually phasedisplaced by Modulated pulses generated at the electrode 35 of the tube34 are fed to a transmitter 39.

A gating device is shown in block form at G1, Gs and G3 in Figure 2 andone of these, namely G1, is shown in detail in Figure 3. VFor clearnessonly three sections, G1, G2 and G3 are shown in Figure 2. Thearrangement of Figure 2 requires twelve such sections, i. e. four timesthe number shown, the other sections being referred to later as G4, Gsetc.

Referring to Figure 3, the circuit comprises, for each channel one valve4I] and one valve 4I For reasons to be explained later, each section,such as that of Figure 3, handles ve channels` spaced apart at intervalsof 24 channels. Thus the ve channel pulses handled by the circuity ofFigure 3 are numbers As, A29, Ass, A17 and Aiui'as www nel concernedwith1 reference to pulses A in Figure 1. Gating pulses, in a negativesense, oc- Curring at the instantsl when eachnchannel is e requiredv to,be operative, and hence at 9 kc./s.,

are derivedfin a manner to be described later,

` andapplied through terminals D5, Dz9e'tc. to the Acontrol gridevor"theyalves 4I, thejscreengrids `ofthe valves lll `are connected tothecontrol w grids of the correspondingvalves Ml., and.` the janodes of thevalves 4| are connected lto the lsuppressor grids oftheccrrespondingvalves 4e.

Boththe suppreseor andvcontrol grids l the valves @le are'rnaintainedbythe'` action fof the A valves di suiiciently negative to 'cut oil" theelec- Ytron current in the valves 4U. When a` negative gating pulsearrives at the controlA grid of L one of `theyalves 4i, for instance atterminal D5, the

small current previously flowing in this valve 4i is out oli, Vthenegative biasis removed simultaneously from the control `and suppressorgrids of the valve le in channel A5 and signals from S are passed totheV anode vof thevalveand to terminal M5. All the anodes ofthe valves40 are connected in common to this terminal M5.

1 Referring again to Figure 2, the cathode rays in the tubesfze and 2'u`are rotated at 9000 revolution per vsecond and a square wave oscillationat 45 kon/s. serves to `deflect the ray from one ring of five anodes tothe other ring of five anodes. VA pulse is therefore generated at eachet these Yanodes once in every 1,@000 second.

are in all twenty anodes, sixty channels can be handled. Theseare theodd-numbered channels and theeven-numbered-channels are dealt with by aduplication of parts ofthe vapparatus'to be specied later.

vIn.. Figure l, only ten trains of pulses D5, D11 etc., are shown. Infact there `are twenty such trains extending over the pulse recurrenceperiod of 1,() r'nillisecond from D5 to D119 inclusive.

.The connections between the sections G1, G2 andGs of the gating deviceand the distributor 25 are shown in Figure 2. The correct connections.between the other sections G4, VG5 etc. will be evident from thereferences given to `the leads from each of the anodes of the devices 25and 25. Thus as shown one group` of anodes (say those around the outerannulus) of the device 2s cao-operates-with gatingsectionsGi, 'G2 andG9, the other group of anodes from' the device 25 co-operates with thegating4 sections Gv, G5 and G9. The outer group of anodes of the device2G co-operates with sections G4, G5 and Gs and the inner group of anodes`of device 26 cooperate with the sections Gio,'G11 and G12.

The terminal M5 of Figures 2 and 3 is connected to one modulatingelectrode ofthe modulator M in Figure 2. As shown in Figure 2,corresponding terminals Mv and M9 of gating sections Gz and G9 areconnnected` with other modulating 'electrodes of .the modulator M. 'Theconf L'other. gating sections and,y the `nroiulator M will beuhderstoodfrom the'referencesgiven` tothe leads .to the modulatorlelectrodes.

Each of the pulse trains D5, D11 etc, in` Figure l is, as stated,intendedtocol-ope'rate with. three channels. Thus train D5co-operatesrwith channels A5, Amand A9; trainDu withz channels A11, A13and Anand soon'.

Consider the, `instant -when 4 it sIeQuiredUthat channel As` should beoperative. A4Atthis `moment a. pulseV D5 isV operativeonthecontroLgridoi' valve lil in channel A5 of theygating device in Figure 3. Thevoltageat M5tl1efeforefcorresponds, to the instantaneous Hvalue of thesignal applied at S5.V This voltage iaappliedgiromltls to. one.modulator electrode ofthe.m'oiulator in Figure 2` and determines theinstantat which a negative pulse A5 (Figure l) occurs at` the anodeofthe modulator M. VTlhechannelpulse A5 considered recursat.aufrequency,of` 9` kc./s. and consequently` every l/9000secondthereis transmitted a pulse whose location intime` denes theinstantaneousvalue of the signal voltage. rlhe effect is substantiallythat `oiawpulse moving in timeabout a mid position,`the limitsci suchmovementbeing determined'` bythe channel widthin this` case aboutl0.2925 microsecond.

Immediately after. the tirneallotted ,tozchannel A5 has passed thatallotted to As begins. ,This is an even-numbered pulse dealt withbyadditions to thecircuitolFigureZ,to be referred to` later. After this`comesthe turnof ,channel A7. At this time a pulse ofthe trainD5isrstillfoper-f ative on the valve 4I ,ochannel Av' .which will .be insection G2. The corresponding ,valve is therefore renderedkoperative andaninstantaneous signal voltage corresponding to' the signal at S7 (Fig.2) will appear .at Mviandon` the corresponding modulating electrode lofM.

It will be noted that lsince the D pulses each serve toopen'threeadjacent odd channels, -signal voltagesof threeadjacentroddchannels `appear upon corresponding modulating; `electrodes of themodulator M.` Thus for `exainplefelectrodes M5, M7 and M9 areallsenergised at the saine time. This does notresult` neon-usion ofthesignals of the threefchannels because the cathode ray beam of the deviceM, cornes under the influence of the different modulatingv electrodes inturn: when it is `underthe influence of electrode M5, it is in theregion of the slotin the plate 3 corresponding to'channel 5. A momentlater when the ray is' in. the-region ofthe slot of channel 1, it isunder the influencent thev elecn trode M7 and not of electrode'M5 or M9and so on.

The distributors 25 and 26 of Figure 2 must be correctly phasedrelatively-to one another insuch a manner `that engagement with theanode D11, 13, 15 of distributor, takes place between en-l gageinentswith the anodes D5. maand D17, is, 21 of `distributor "25. lForthispurpose one of :the distributors may be rotatablefrelatively to itsdeflectingcoils l23,1 22er` electrical phase .adjusting means may 'beprovided foradjustingthe phase of the ACurrents fed to the coils'28 and29 of one tube relatively to that Afed `to the coils of the othertube.

S0 `far there has been described a system for handling channels whichare the odd A channels shown in Figure 1. In this system the number ofcliannelsNO, the channel,pulse` recurrence frequency F=9 kc./ s., and.thenumber ,of

1 equally spaced channels operated by onecglfianrief medulai'"that-15111.01 ser tu. is .5.- Sinee the modulator M has 12 slots eachofwhich operates with ve channels; for example M operates with channelsA5, A29, A33, A77 and A101, these channels being equally spaced. Thechannels handled by six of the twelve modulating electrodes o1 thedevice M are shown by the wave forms M1, Ma etc. in Figure 1.

For the even numbered channels, it is clearly possible to use the same Dpulses as for the odd channels. The minimum addition to the apparatus ofFigure 2, is therefore, one further modulator tube M and twelve furthergating sections Such aS G1 t0 G12.

It is possible to use D pulses of longer duration and to use fewerdifferent tra-ins of D pulses.

, Each pulse train then handles more than three channels of the sixty(or more than six of the hundred and twenty). It is, however, necessaryto ensure that there can be no overlap between the D pulses handling twochannels spaced by 24 or more, for instance 'A5 and A29, since suchchannels are dealt with by a single modulator, in this example Ineffect, by the use of the invention, there is obtained a multiplicationof the number of channels that can be handled by a given modulator. Suchmultiplication can be repeated by the use of further distributors withco-operating gating circuits effectively in series with those shown inFigure 2.

Instead of providing a single deflecting means for each channelmodulator M5 etc., a plurality of such means (e. g. deflecting plates orpairs of vdeiiecting plates) may be provided in associa-- tion with eachslot in the plate 35 of Figure 2, the deflecting means being disposed atdifferent points along the cathode ray beam. Each deflecting means maybe arranged to deal with one or more channels and the associateddistributors are modified accordingly. It is preferably arranged, bysuitable spacing cf the deiiecting plates or by feeding suitablydifferent signal amplitudes to the individual deflecting means,

that all have approximately the same sensitivity.

Instead of the master generator I0 being one operating at the higherfrequency, it may operate at the lower frequency (in the example 9kc./s.) and the higher frequency (in the example 45 kc./s.) maybeobtained therefrom by frequencymultiplication.

Demodulation at a receiver is accomplished in an analogous manner to themodulations.

One receiving arrangement will be described by way of example withreference to Figure 5. The received signals of the character shown at Ain Figure 1 are applied at 45 to a synchronizing signal selector i? ofany known or suitable type which selects the synchronizing signals fromthe channel pulses and separates the 9 l:c./s. synchronising pulses (AI)from the remaining` synchronising pulses. Typical synchronizing signalselectors are disclosed in the following British patents: 407,951-Fig.4, circuit No. 3; and page 3, lines 43-52; 470,495-Fig. 5, valve 16; andpage 12, lines 36-47 422,906-Fig. 9, valve 16; and page ll, line 104,page 12, line 3; 534,729--circuit including valves 42. 43, 45 and 46;and page 9, lines 49-88. The selector also furnishes synchronisingpulses at 45 lac/s. corresponding to the pulses A1, A25, A40 etc. usedto Vcontrol the frequency of an oscillation generator 48 (it may use acircuit like that of the squares I6, Il), the second harmonic of Whoseoutput, namely 90 kc./s..,is selected. This is frequency-multiplied byfurther harmonic selec- The latter pulses are tion in a multiplier 49,the 6th harmonic at 540 kc./s. being selected. Two sine waveoscillations at 90 kc./s. in quadrature produced from the oscillationgenerator 48 by a phase-splitter 5i) (whose circuit is like that of thephase-splitting portions of the devices II, 22) are applied to deilectthe cathode ray of a distributor 5I in a conical path over sixelectrodes E1, YYE2 Ee respectively, and a rectangular Waveformoscillation at the 540 kc./s. frequency from a squaring circuit 52(whose circuit is like that of the square I6, Il) fed from the frequencymultiplier 49 is applied to the control electrode of the distributor.The deilecting means of the distributor are made adjustable relativelyto the distributor tube, or, as indicated in Figure 5, electricphase-adjusting means may be incorporated in the circuit 55.

Assuming that the arrangement is such that pulses are generated at theelectrode E1 at the instant of occurrence of channel I, then pulses aregenerated at the same electrode at the instant of occurrence of channelsI3, 25, 31 and so on to 59. At electrode Ez the pulses generatedcorrespond to channels 3, I5, 2l etc. to III and so on for the remaindero1 the six electrodes. These pulses serve as gating pulses to selectchannel pulses from one another.

Six selectors are provided, one associated with each electrode E1, E2etc. although, for clearness, only that associated with electrode E1 isshown. Each such selector may consist of a pentode valve 53 having thereceived signals applied in a negative sense to the control grid, andhaving the pulses E1 or E2 etc., as the case may be, applied to say thesuppressor grid. The pulses applied to the suppressor grid must bepositive in sense. This may be achieved either by arranging that thesecondary emission from the electrodes E1, E2 etc. exceeds the primarycurrent reaching the electrodes from the beam or by including betweenthe electrodes and the selectors a phasereversing stage. The pulsesapplied to the suppressor grid serve as gating pulses to pass throughthe selector only those of the channel pulses occurring at the instantsof occurrence of pulses on the suppressor grid. In the case of electrodeEi the selector associated therewith passes channel pulses I, I3, 25etc. The output of each selector is connected to a converting device forconverting pulse-time into pulse-Width modulation. The device may, forexample, be as described in the specification of co-pending UnitedStates patent application No. 11,368 iiled February 27, 1948, by MauriceMoise Levy. Thus it may comprise, as shown in Figure 5, a diode 54having connected to its cathode a resistor 55 in parallel with acondenser 55. This resistor-condenser combination is arranged to have atime constant long compared with the channel width. The voltage acrossthis resistor and condenser is applied to the anode of a second diode5'! having a resistor 53 connected to its cathode. Squared pulses at 540kc./s. are applied from the squarer 52 to the cathode of the diode 5? ina positive sense. When a pulse passed by the selector 53 reaches theanode of the diode 54 the condenser 55 is charged rapidly because thediode 51 is at that time held non-conducting by the pulse from 52. Whenthe channel pulse ceases Ythe condenser 56 substantially retains itscharge until the pulse from 52 ceases when it is rapidly discharged. Thewidth-modulated pulses are obtained at the anode of the diode 5l, theirleading edge (in this example) varying in time of occurrence inaccordance with the time of occuraeaasse reassess keine siedi-linien; ofaerienne pulses and their'` trailing edgeoccurrihgjat iixed. regulai'aminstants ,determined the trailing edges' i `thepulses'from,52". Thelatter pulses are. of course, arranged to .have 'their "leadingedgesoccurring not later than the earliest instants oi occuri'ence'fof thelc'orresponding channel. pulses.. The anode "of the diode El" isYconnected to thev 'il through a phase'splitter [Sil (whose circuit islike that of the phase-splitting `portions oi' the devices H, 22). `Eachoi. the'output electrodes is coupled through a separator valve E! and alov-J pass ltei'iii to an output terminal 63, the filter serving, `inlmown manner, to "derive the modulation,` from the Width-modulatedpulses.

Only theseparator valve and nlter associated withnne of the electrodes His shown in Figure'.

The distributor associated with the E1 pulses u". respectively themodulations of" the ten channels i, l3 ,25 IESS.

A separateseleotor yconvertingdevice 5f3-`53 andftenl-electrodedistributor 59 is required for each of the electrodes E2 E5 and hencesix'such combinations are required for the odd numbered channels.

'Ihe even-numberedfchanneis' require a iurther six-electrode distributorto the control electrode. of vvhich are fed oscillationsxat`540 kc./s.in thel'opposite 'phase to that used for the oddnunibered channels, andsix further selectors,`

converter devices and ten-electrode distributors.

Many variations in the particular receiving arrangement described can ofcourse be made. The numbers of electrodes on the distributors and hencethe numbers of distributors may be varied and moreover other kinds oidistributor may be used.

In any case the arrangement can be made such that a step in thedemodulation process, in the above example conversion from time to Widthmodulation, is performed upon a group of pulses of different channelsbefore the separation of the individual channels of the group from oneanother. This results in a considerable economy of apparatus.

Instead of converting the time-modulation to Width modulation, it may beconverted to amplitude-modulation, and the modul-ation may then bederived by means of a low-pass filter `as in the case of Widthmodulation, or otherwise.

The invention Whether used in transmitting; or receiving is not limitedto the use of the particular forms of modulator, demodulator anddistributor described, nor to the use of electronic modulators anddistributors, or to the use of time pulse modulation. Width modulation,obtained by triangular slots, or double time modulation, obtained by twoslots having a V shape, with the advantage of lower distortion, may beused.

Other known or suitable devices may be used.

We claim:

l. A multi-channel pulse signalling system for operating up to Nchannels each at the same recurrence frequency, said channelsconstituting N/a groups each of a equally-spaced channels, where a is aninteger greater than unity, Isaid system comprising means for theuni-directional inter-conversion between modulated and lunthus furnishatt-he ten output terminalst3` f modulated pu1ses`,' said mea-nsfVincludingcjd vices for at least`par`tiallyeiectingsuch. inter-,-conversion, and distributor means `for Acoupling insuccession-to each ofsaid devices the channels of al different `one of `said groups.,

2. A system according to `claim 1, wherein Aeach` device is a modulatorand" each ucvshannell consti--A tutes a source of. modulating signals,and Wherein means is provided to generate pulses to be modulated.A

3. A system according te eiaimi, whcisseh;

device is a partofz a demodulator, and v'vhcrein there'areprovidedselectorsfor separating "ref-, ceived. pulses.V into said` `groups and,means Qfor-. applying received modulated pulses to said sele'cl" tors..n n Y, e., A systemA according time-modulated pulses into'Awidth-modulated pulses.

N/a groups each. of a equallyspacedchannels,

Where ais aninteger greater'than unity, saidsys-- tem comprisingacathode raytubepulsemodulator system including.N/amodulators and means.-

to sweep the cathode ray beamnof said tube, into cooperation with said'modulators-in. reculrifingA succession to generate apulse in each. ofsaid..` modulators ateach such cooperation,`N source-S., I of modulatingsignals, and a cathode Srayjtubel l distributor'to apply signals fromcof said sources successively to each of said modulatgirstd moduf` latesuccessively pulses in said modulator respe'cv` tively.

6. A multi-channel pulse signalling system for operating up to Nchannels each at the same recurrence frequency said channelsconstituting N/a groups each of a equally-spaced channels, where a is aninteger, said system comprising N/a. sets each of a gating devices eachpassing to the output thereof only such of the signals impressed thereonas occur during the presence of gating pulses, means for impressingsignals from diierent channels continuously upon diiierent gatingdevices respectively, means for generating trains of gating pulses ofthe said recurrence frequency and displaced in time relatively to oneanother, means for applying said trains to said gating devices tocontrol the passage of signals through such devices, the gating pulsesapplied to each set being free from overlap in time, N /a modulatingdevices, means for rendering said modulating devices operative insuccession to produce pulses modulated in accordance with signalsapplied thereto and means for coupling the output of one of said sets ofgating devices to each said modulating device, whereby the successivepulses from each of said modulating devices are modulated in accordancewith a different one of said channels.

7. A multi-channel pulse signalling system for operating up to Nchannels each at the same recurrence frequency, said channelsconstituting N/a groups each of a equally-spaced channels, where a is aninteger, said system including a receiver or time-modulated pulsescomprising means for generating N/c trains of gating pulses, such trainsbeing equally spaced in time, means for synchronising such pulses inaccordance with received synchronising signals, N/a gating devices eachhaving an input circuit for received signals, an output circuit and acontrol circuit r `to claini, wherein,re.- ceired pulses aretimeflmodulated," and .wherein eachl device comprises .a circuit'fforconverting for the yapplication of gating pulses to permit the passageof said received signals to said output circuit only during said gatingpulses, means for applying said trains of gating pulses to said controlcircuits respectively, N /a circuits for converting time-modulatedpulses to Width-modulated pulses, means for connecting each said outputcircuit to -a'diiTerent one of said converting circuits, N demodulatorsfor extracting the modulation from Width-modulated pulses, distributormeans for coupling each of said converting circuits to a, of saiddemodulators in succession.

8. A transmitter for multi-channel pulse signalling for transmittingsignals from up to N channels each by a train of pulses, the pulses ofthe trains having the same pulse recurrence frequency, said channelsconstituting N/a groups each of a equally-spaced channels, where a is aninteger greater than unity, said transmitter com pri-singN/a modulatingdevices for modulating pulses in dependence upon signals applied to amodulating terminals thereof, and distributor means vfor coupling insuccession to each of said modulating terminals the channels of adiierent one of said groups. f

9. A transmitter for multi-channel pulse signalling for transmittingsignals from up to N channels each by a train of pulses, the pulses ofthe trains having the same pulse recurrence frequency, said vchannelsconstituting N/a. groups each of a equally-spaced channels, where a i-san integer greater than unity, said transmitter comprising a cathode raytube modulator system including N/a modulating devices, and means tosweep the cathode ray beam of said tube into cooperation With saidmodulating devices in recurring succession to generate a pulse in eachsaid l2 modulator at each such cooperation, N sources of modulatingsignals, and a cathode ray tube distributor system to apply signals fromeach of y MAURICE MOISE LEVY. DENNIS CLARK ESPLEY.

REFERENCES CITED The following references are of record in the iile ofthis patent:

UNITED STATES PATENTS Number Name Date 2,036,350 Montani Apr. 7, 19362,041,245 Haicke ,May 19, 1936 2,205,406 Holcomb June 25, 1940 2,395,467Deloraine Feb. 26, 1946 2,418,116 Grieg Apr. 1, 1947 2,423,466 PetersonJuly 8, 1947 2,429,631 Labin et al Oct. 28, 1947 2,474,810 Arditi et alJuly 5, 1949 2,499,534 Sorber Mar. '7, 1950 2,499,844 Boothroyd Mar. 7,1950 2,513,335 Labin et al July 4, 1959 2,517,365 Von Baeyer Aug. l,1950 2,549,826 Labin Apr. 24, 1951 OTHER REFERENCES Pulse Time ModulatedMultiplex Radio Relay System Terminal Equipment, ElectricalCornmunication, vol. 23, June 1946, pages 159-178.

